Apparatus for preventing lightning strike damage to a structural component

ABSTRACT

Preventing damage to a metal component or reducing manufacturing assembly steps. An initial channel, defined by an inner surface, is formed through the metal component. A bushing is placed into the initial channel, the bushing having an outer surface and an inner channel. An interference fit is created between the outer surface and the inner surface. A final channel is formed through the bushing. In forming the final channel, material is removed from the bushing to increase a size of the inner channel to be suitable to receive a fastener and such that the inner surface of the metal component remains unexposed within the final channel. The final channel extends through a second component. A fastener is placed into the final channel to attach the metal component to a second component, wherein electrical magnetic effects occur between the fastener and the bushing.

This application is a continuation application of U.S. application Ser.No. 11/468,174, filed Aug. 29, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to airplanes and moreparticularly to reducing electro-magnetic effects to structuralcomponents in an airplane in addition to reducing the number of stepsneeded to assemble components.

2. Description of the Related Art

Lightning strikes occasionally occur on an aircraft traveling near orthrough a thunderstorm. A lightning strike on an aircraft normally doesnot damage the aircraft, but may leave a burn mark. Additionally, pitsor burns on the skin of the aircraft occur at points of entry or exitfor the lightning strike. In particular, an electric strike arcing mayoccur between a fastener and a hole bore in a structure in whichfasteners are used to hold different structural components of theaircraft together. The arcing may induce a defect on the surface, whichinduces a stress concentration. This defect is also referred to as“pitting”. Various parts of the aircraft may be more sensitive to thistype of defect than others. For example, the side-of-body chord used toattach a wing to the aircraft is often made of titanium. Holes areformed in the side-of-body chord to receive fasteners to attach thewing. This type of metal is very notch sensitive.

As a result, pitting on a hole surface in a chord made of titaniumgreatly reduces the fatigue resistance of this part. This component andother components for the side body joint are part of a safety of flightjoint and cannot have these types of defects.

One current approach to reduce electro-magnetic effects (EMEs), such asthose from lightning strikes, is to use interference fit fasteners.However, with the currently used assembly processes, interference fitfasteners are hard to use because of space constraints present wheninstalling the fasteners while attaching a wing to a body of anaircraft. Redesigning the joint is expensive and not feasible.

Current assembly processes employ “One-Up Assembly” in which once partsare put together, the different parts are not taken apart again. Thecomplexity with the number of different fasteners makes it almostimpossible to correctly realign parts if parts have to be removed oncethey have been put together in the assembly process. For this reason,“One-Up Assembly” is often used. For example, in attaching a wing to abody of an aircraft, several thousand fasteners may be required toattach the wing to the body. Realigning this number of holes forfasteners is very time consuming if the parts are taken apart afterholes are created for fasteners to remove defects that occur fromcreating the holes for the fasteners. In most cases realignment isimpossible if disassembly occurs.

Therefore, it would be advantageous to have an improved method andapparatus for assembling components.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a method and apparatusfor preventing damage to a metal component that is susceptible to damageby electro-magnetic effects. An initial channel is formed through themetal component. The initial channel is defined by an inner surface. Abushing is placed into the initial channel, wherein the bushing has anouter surface and an inner channel. An interference fit is createdbetween the outer surface of the bushing and the inner surface of theinitial channel through the metal component. A final channel is formedthrough the bushing. In forming the final channel, material is removedfrom the bushing to increase a size of the inner channel to one that issuitable to receive a fastener and such that the inner surface of themetal component remains unexposed within the final channel. The finalchannel extends through a second component. A fastener is placed intothe final channel to attach the metal component to a second component,wherein electro-magnetic effects occur between the fastener and thebushing.

The features, functions, and advantages can be achieved independently invarious embodiments of the present invention or may be combined in yetother embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives and advantages thereof, willbest be understood by reference to the following detailed description ofan advantageous embodiment of the present invention when read inconjunction with the accompanying drawings, wherein:

FIG. 1 is a diagram of an aircraft in which an advantageous embodimentthe present invention may be implemented;

FIG. 2 is a diagram illustrating structural components used to affix awing to a body of an aircraft in accordance with an advantageousembodiment of the present invention;

FIG. 3 is a cross-sectional diagram illustrating a fastener inaccordance with an advantageous embodiment of the present invention;

FIG. 4 is a cross-sectional diagram of a fastener in the form of atitanium stud in accordance with an advantageous embodiment of thepresent invention;

FIGS. 5A-5C are cross-sectional diagrams illustrating the installationof a bushing within a titanium section in accordance with anadvantageous embodiment of the present invention;

FIGS. 6A-6B are cross-sectional diagrams illustrating fastening twostructural components together in accordance with an advantageousembodiment of the present invention;

FIG. 7 is a cross-sectional diagram illustrating bushing offsetcapability in accordance with an advantageous embodiment of the presentinvention;

FIG. 8 is a diagram illustrating offsets in the positioning of adiameter in a hole within a bushing in accordance with an advantageousembodiment of the present invention;

FIG. 9 is a cross-sectional diagram illustrating securing a bushing to aplate in accordance with an advantageous embodiment of the presentinvention; and

FIG. 10 is a cross-sectional diagram illustrating a bushing inaccordance with an advantageous embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to the figures, and in particular, with reference toFIG. 1, a diagram of an aircraft is depicted in which an advantageousembodiment of the present invention may be implemented. Aircraft 100 isan example of an aircraft in which a method and apparatus for preventinglightning strike damage to a structural component may be implemented.Further, aircraft 100 also illustrates an example of an aircraft inwhich the number of steps needed to fasten the structural componentstogether is reduced.

In this illustrative example, aircraft 100 has wings 102 and 104attached to body 106. The attachment of wing 102 and wing 104 to body106 are examples of structures in which protection from electro-magneticeffects, such as lightning strikes, is crucial to maintain fatigueresistance. Typically, body 106 has a side-of-body chord (not shown)that is made of titanium and used to join wing 102 and wing 104 to body106. In this depicted example, these wings have carbon fiber reinforcedpolymer (CFRP) within the structural components. Aircraft 100 includeswing mounted engines 108, 110, 112 and 114. Further, aircraft 100 alsoincludes body mounted engine 116 body mounted engine 118 and tail 120.

Turning now to FIG. 2, a diagram illustrating structural components usedto affix a wing to a body of an aircraft is depicted in accordance withan advantageous embodiment of the present invention. In this example,these structural components show the point at which a wing, such as wing102 in FIG. 1, is affixed to a body of an aircraft, such as body 106 inFIG. 1.

In this illustrative example, wing 200 is affixed to a wing box for thebody of the aircraft using chord 204, chord 206, and splice plate 208.In these examples, fasteners, such as bolts 210, 212, 214, and 216 areassembled using bushings in accordance with an advantageous embodimentof the present invention. Assembly of fasteners, such as bolts, isdescribed in more detail below.

The present invention provides a method and apparatus for preventingdamage to a metal component that is susceptible to damage byelectro-magnetic effects. In these illustrative examples, theelectro-magnetic effect is one caused by a lightning strike on anaircraft. In attaching components to each other, an initial channel isformed through a metal component. This metal component has an innersurface. A bushing is placed into this initial channel. The bushing isexpanded to form an interference fit between the outer surface of thebushing and the inner surface of the channel formed in the metalcomponent. A final channel is formed through the bushing and the secondcomponent in which material is removed from the bushing to increase thesize of the inner channel.

This increased size of the inner or final channel is suitable to receivea fastener. Further, the inner surface of the metal component remainsunexposed within the final channel. The fastener is placed into thefinal channel to attach the metal component to the second component. Asa result, in the event that an electro-magnetic effect occurs, theelectro-magnetic effect occurs between the fastener and the bushinginstead of between the fastener and the metal component. Further, themetal component may be placed into position for attachment to the secondcomponent prior to forming the final channel. This step is anillustrative example of one that helps facilitate “One-Up Assembly”.

Turning now to FIG. 3, a cross-sectional diagram illustrating a fasteneris depicted in accordance with an advantageous embodiment of the presentinvention. In this example, the fastener takes the form of bolt 300.Bolt 300 is an example of a bolt, such as bolt 210 in FIG. 2. As can beseen in this example, carbon fiber reinforced polymer (CFRP) section 302and titanium section 304 are two different components that are joinedtogether.

As depicted, bushing 306 forms a barrier between bolt 300 and titaniumsection 304. In this illustrative example, bushing 306 provides asacrificial material in the event of an electro-magnetic effect, such asa lightning strike. Any arcing that may occur from a lightning strikeoccurs between bolt 300 and bushing 306 in these illustrative examples.In this manner, any damage or pitting, that may occur, occurs in bushing306, rather than in titanium section 304.

Bolt 300 is secured using washer 308 and nut 310. As used herein, abushing is a cylindrical shell with or without a flange that may beinstalled in a structural component in conjunction with a member orfastener, such as a pin or a bolt. In other words, a bushing is a memberthat is cylindrical in shape and has a channel through it. The outsidesurface of this member has an outer diameter and the channel has aninner diameter. A bushing is also referred to as a plain journal bearingor a sleeve bearing in these examples.

Bushings are typically used for components that move or turn. In theillustrative examples, however, these bushings are used as a sacrificialmaterial for placing fasteners, such as bolts, into materials that aresusceptible to damage from electro-magnetic effects. One example of thistype of material is titanium. Other examples of materials that may beused include aluminum and steel alloys. Arcing will reduce the fatiguelife of any metal component.

Turning now to FIG. 4, a cross-sectional fastener in the form of atitanium stud is depicted in accordance with an advantageous embodimentof the present invention. In this example, titanium stud 400 holdstogether carbon fiber reinforced polymer section 402 and titaniumsection 404. Titanium stud 400 is surrounded by bushing 406 withintitanium section 404. Titanium stud 400 is held in place using nut 408,washer 410, nut 412, and washer 414. Titanium stud 400 is an alternativeexample of a fastener that may be used in accordance with anadvantageous embodiment of the present invention. The fasteners shown inthe examples in FIGS. 3 and 4 are presented for purposes of illustrationand are not intended to limit the type of fastener that may be used inthe different embodiments of the present invention.

Turning now to FIGS. 5A-5C, cross-sectional diagrams illustrating theinstallation of a bushing within a titanium section are depicted inaccordance with an advantageous embodiment of the present invention.

In FIG. 5A, hole 500 is formed in titanium section 502. Hole 500 iscreated through a drilling process in these examples. This hole is afirst channel in titanium section 502. One result of the drillingprocess is that burrs are present both in entry 504 and exit 506 of hole500 in titanium section 502. In this illustrative example, de-burring isthen performed on titanium section 502 to remove these defects. Thesedefects are removed to avoid fatigue penalties in metal materials, suchas titanium. Thereafter, in FIG. 5B, bushing 508 is installed into hole500 in titanium section 502. Bushing 508 contains hole 510, which formsa second channel. This hole is one through which a fastener may beplaced.

In FIG. 5C, mandrel 511 is pulled through bushing 508 to expand bushing508 such that it remains in place in titanium section 502. Theinterference fit is between outer surface 512 of bushing 508 and innersurface 514 of hole 500 in titanium section 502. An example of a processthat may be used to generate an interference fit for a bushing isForcemate available from Fatigue Technology, Inc. Of course, aninterference fit may be accomplished using other tools or processes. Forexample, currently available shrink or press fit processes may be usedto create the interference fit.

Turning now to FIGS. 6A-6B, cross-sectional diagrams illustrating thefastening of two components together are depicted in accordance with anadvantageous embodiment of the present invention. In these illustrativeexamples, the components are structural components. In this example inFIG. 6A, titanium section 600 contains bushing 602 and is similar to thefinal titanium section, titanium section 502, depicted in FIG. 5C.

In FIG. 6A, carbon fiber reinforced polymer (CFRP) section 604 isbrought into place with titanium section 600. Thereafter in FIG. 6B,drill 606 is used to form hole 608 in CFRP section 604. Hole 608 hasbeen drilled or bored to increase its size to form a final channel forfinal attachment. Bushing 602 serves as a guide for drill 606 increating hole 608. These two sections form stack 610.

In creating hole 608, a burr present in inner diameter 612 of bushing602. This burr is caused by reaming performed to increase a size of thediameter of hole 608 to inner diameter 612. However, a burr is notpresent within titanium section 600. This burr does not have to beremoved because the burr is in bushing 602, not in titanium section 600.

As a result, fatigue penalties are not incurred in this process.Further, this type of process also allows for “One-Up Assembly”. “One-UpAssembly” is a process in which the structure is not separated after ithas been put together. In other words, stack 610 does not need to bedisassembled to de-burr or remove the burr created within bushing 602.Stack 610 is left as is after the drilling occurs.

Consequently, an extra step in which disassembly of the components andcleaning or de-burring is avoided by using the processes in anadvantageous embodiment of the present invention. This final reaming ordrilling within hole 608 forms the final channel through bushing 602.The fastener is placed into this final channel formed within hole 608.The point of origin for a diameter of the final channel created throughthe bushing does not have to follow the point of origin for the diameterof the original hole created by the bushing as long as the componentthat is to be protected is not exposed. The thickness in the wall of thebushing varies depending on the particular requirements andimplementations.

Although the depicted examples are shown in which the final channel fora fastener is created after the components have been brought togetherand aligned, the different advantageous embodiments of the presentinvention may be applied to components in which the final channel isgenerated separately for the components. In this type of implementation,the components are aligned after the formation of the final channel.Although additional steps may occur with this type of implementation,the bushing still serves to protect the material for the component forwhich damage from electro-magnetic effects is to be avoided.

Turning now to FIG. 7, a cross-sectional diagram illustrating bushingoffset capability is depicted in accordance with an advantageousembodiment of the present invention. In this example, stack 700 includestitanium section 702, carbon fiber reinforced polymer (CRFP) section 704and titanium section 706. In this example, titanium section 702 containsbushing 708 and titanium section 706 contains bushing 710.

As depicted, the walls of bushing 708 have an even thickness throughout,while the walls of bushing 710 have an uneven thickness. Thesedifferences between the thickness of the walls in bushings 708 and 710provide for increased part alignment tolerance. The thickness of a wallin a bushing may be less in some places than others as long as thethickness is sufficient to prevent electro-magnetic damage fromoccurring in the particular titanium section.

With reference now to FIG. 8, a diagram illustrating offsets in thepositioning of a diameter in a hole within a bushing is depicted inaccordance with an advantageous embodiment of the present invention.This diagram illustrates a cross-section of a bushing in this example.Bushing 800 has outside diameter 802 and original inside diameter 804.Center point 806 is the point of origin for outside diameter 802 andoriginal inside diameter 804. Final inside diameter 808 may have adifferent point of origin that is offset from center point 806 in thisillustrative example. As can be seen, final inside diameter 808 for thefinal channel in which a fastener is placed does not have a point oforigin along center point 806. This offset occurs to allow for partalignment tolerances to increase between the different parts being puttogether in a stack, such as stack 700 in FIG. 7.

Other offsets for the point of origin from center point 806 may occurdepending on the particular alignment. The minimum distance betweenfinal inside diameter 808 and outside diameter 802 depends on theparticular implementation.

Turning now to FIG. 9, a cross-sectional diagram illustrating securing abushing to a plate is depicted in accordance with an advantageousembodiment of the present invention. This figure illustrates one mannerin which an interference fit may be created between a bushing and thecomponent in which the bushing is placed.

In this depicted example, bushing 900 has been placed into plate 902.Mandrel 904 is pulled from flange side 906 of bushing 900 through tonon-flange side 908 of bushing 900 in the direction of arrow 910 to forman interference fit between bushing 900 and plate 902. This type ofsecuring of bushing 900 results in stress occurring in plate 902 becausebushing 900 becomes slightly deformed. In particular, the diameter onnon-flange side 902 expands more than the diameter on flange side 906.As a result, reversing the direction in which mandrel 904 is pulled tothe opposite side of flange side 906 results in less distortion orstresses on plate 902.

Turning now to FIG. 10, a cross-sectional diagram illustrating a bushingis depicted in accordance with an advantageous embodiment of the presentinvention. In this example, a cross-section of bushing 1000 is depicted.Flange side 1002 of bushing 1000 has inner diameter 1004, whilenon-flange side 1006 has inner diameter 1008. Inner diameter 1004 isless width than inner diameter 1008. A tapering is present to increasethe diameter on non-flange side 1006 within bushing 1000. This taperingis used in this illustrative example to account for a differentexpansion within bushing 1000 when a pull of a mandrel from flange side1002 on non-flange side 1006 occurs in securing bushing 1000 to a plate.This geometry is selected to provide a uniform radial expansion in thebushing when an interference fit is created using a tool, such as amandrel.

This differential expansion occurs because of the stiffness of theflange. Another reason for the differential expansion is becausematerial from the inside diameter of bushing is pulled through the holeas the mandrel expands the bushing. This material creates more radialmovement at the outside diameter and into the titanium on the exit sideof the mandrel. Opening up or increasing the inside diameter of thebushing near the exit side on or increasing non-flange side 1006 createsa more uniform radial expansion. In particular a more uniform radialdisplacement of the outside diameter of the bushing in the metalcomponent. The key, in these examples, is to modify the pull directionand/or bushing geometry to obtain more uniform radial or expansiondisplacement in the metal component in which the bushing is placed. Theoverall focus is the have a radial expansion in the bushing that reducesdeformation or distortion in the metal component from creating theinterference fit.

Further, although the pulling of a mandrel through a bushing is shown inthese advantageous embodiments as a mechanism for securing a bushing toa structure in which the bushing is inserted, other methods may be usedto create an interference fit depending on the particularimplementation. For example, bushings may be placed into liquid nitrogensuch that the bushings shrink in size. These bushings are then placedinto the holes within the structures. As the bushings increase intemperature, they expand and become secured within the holes in thestructures in which they have been placed.

Thus, the present invention provides a method and apparatus forpreventing damage to a metal component that is susceptible to damage byelectro-magnetic effects such as a lightning strike. An initial channelis formed through a metal component. A bushing is placed into theinitial channel. An interference fit is created between the outersurface of the bushing and the inner surface of the initial channel inthe metal component. A final channel is formed through the bushing inwhich material is removed from the bushing to increase a size of theinner channel. This inner channel has a size that is suitable to receivea fastener to fasten the metal component to a second component. Further,the inner surface of the metal component remains unexposed in the finalchannel. The bushing serves as a barrier between the fastener and themetal component within the final channel. A fastener is placed into thefinal channel to attach the metal component to the second component.

In these illustrative examples, the bushing acts as a sacrificialmaterial, such that the process for placing fasteners within thetitanium plate does not require drilling of the titanium itself.Instead, the drilling occurs with respect to the bushing. In theseillustrative examples, the bushings are made of steel. The bushings,however, may be made of other materials depending on the particularimplementation. For example, the bushing may be made of copper berylliumor aluminum nickel bronze. The particular material used for a bushingwill depend on the particular implementation.

With the use of bushings in securing structures to each other withfasteners, a “One-Up Assembly” process may be implemented, such that astep in which these structures are taken apart and burrs are cleaned orremoved is avoided. This extra step is avoided because any defects aregenerated in the bushing rather than in the structure itself. As aresult, a fatigue penalty is not incurred.

A further advantage of using these bushings is that in the event of anelectro-magnetic effect, such as one caused by a lightning strike, anypitting or damage occurs in the bushing, rather than in the structure inwhich the bushing and the fastener has been placed. As a result, anyarcing between the fasteners occurs with the bushing. The titaniumplates remain un-pitted and undamaged by such an electro-magneticeffect. As a result, any damage or fatigue caused by these effects maybe remedied by removing the bushing and fastener and putting a new onein its place.

Further, the depicted examples in these advantageous embodiments showprocesses and apparatus for fastening two structural components togetherin an aircraft. These embodiments may be applied to any set of two ormore components that are to be fastened together. For examples, theembodiments may be applied to fastening three components together inwhich bushing as used in two components. Additionally, although thedifferent examples show a titanium component and a composite componentbeing fastened together, the illustrative embodiments may be applied toany materials. Moreover, the use of the bushing as a sacrificialmaterial may be applied to any material in which electro-magneticeffects are of a concern. When electro-magnetic effects are not of aconcern, a bushing also may be used as a sacrificial material withrespect to reducing the number of steps needed to assemble or fastencomponents together. The bushing in these examples is the component thatincurs defects, such as burrs, during the assembly process. The materialin which the bushing is inserted avoids these defects.

The description of the present invention has been presented for purposesof illustration and description, and is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the art. Forexample, although the embodiments are directed towards components use inaircraft, the aspects of the present invention may be applied to otherstructures. For example, the embodiments of the present invention may beapplied to automobiles or boats. In fact, the different embodiments ofthe present invention may be applied to fastening any two or morecomponents together with fasteners in which damages fromelectro-magnetic effects is undesirable in one of more of thecomponents. Further, different advantageous embodiments may providedifferent advantages as compared to other advantageous embodiments. Theembodiment was chosen and described in order to best explain theprinciples of the invention, the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. An apparatus comprising: a first sectioncomprising a first material; a first bushing disposed through the firstsection, creating a first channel in the first section; a second sectionin contact with the first section, the second section comprising acarbon fiber reinforced polymer, the second section including a secondchannel in communication with the first channel; a third sectioncomprising a second material; a second bushing disposed through thethird section, creating a third channel in the third section, whereinthe third channel is in communication with the second channel; and afastener disposed through the first channel, the second channel, and thethird channel, wherein the fastener, the first bushing, and the secondbushing are configured such that electromagnetic effects occur betweenthe fastener and at least one of the first bushing and the secondbushing instead of between the fastener and at least one of the firstsection and the third section.
 2. The apparatus of claim 1, wherein thefirst material and the third material both comprise titanium.
 3. Theapparatus of claim 1, wherein first walls of the first bushing have aneven thickness along a first length of the first channel.
 4. Theapparatus of claim 3, wherein second walls of the second bushing have anuneven thickness along a second length of the second channel.
 5. Theapparatus of claim 4, wherein the even thickness and the uneventhickness create a difference in thickness of the first walls and thesecond walls that provide for increased part alignment tolerance.
 6. Theapparatus of claim 1, wherein a first center point of the first bushingis offset from a second center point of the second bushing, relative toa longitudinal axis of the first bushing.
 7. The apparatus of claim 1,wherein the first bushing includes a flange side on a first side of thefirst section, and the first bushing includes a non-flange side on asecond side of the first section, opposite the first side.
 8. Theapparatus of claim 7, wherein the first bushing is expanded on theflange side relative to the non-flange side.
 9. The apparatus of claim8, wherein a first inner diameter of the first bushing on the flangeside is greater than a second inner diameter of the first bushing on thenon-flange side.
 10. The apparatus of claim 9, wherein the first bushingis connected to the first section by means of an interference fit. 11.The apparatus of claim 9, wherein the first inner diameter and thesecond inner diameter are selected to obtain a more uniform radial orexpansion displacement in the first section in which the first bushingis placed, relative to a case where the first inner diameter and thesecond inner diameter are about equal.
 12. The apparatus of claim 1,wherein the first bushing comprises a material selected from the groupconsisting of: steel, copper beryllium, and aluminum nickel bronze. 13.The apparatus of claim 1, wherein the second bushing includes a flangeside on a first side of the second section, and the second bushingincludes a non-flange side on a second side of the second section,opposite the first side.
 14. The apparatus of claim 13, wherein thesecond bushing is expanded on the flange side relative to the non-flangeside.
 15. The apparatus of claim 14, wherein a first inner diameter ofthe second bushing on the flange side is greater than a second innerdiameter of the second bushing on the non-flange side.
 16. The apparatusof claim 15, wherein the first inner diameter and the second innerdiameter are selected to obtain a more uniform radial or expansiondisplacement in the second section in which the second bushing isplaced, relative to a case where the first inner diameter and the secondinner diameter are about equal.